Vapor deposition apparatus



June 17, 1969 5' HIRE-STONE ET AL 3,450,097

VAPOR DEPOS IT ION APPARATUS Filed Sept. 10. 1965 Sheet Z of 2 FIG. I

J 4o FEEDER 2 46 CONTROL FEEDER 52 38 I2 IIIBR W l I n l 32% lp iih...

INVENTORS,

STANLEY FIRESTON'E JOHN MC CARTHY ATTORNEYS June 17, 1 969 Filed Sept.10, 1965 s. FIRESTONE ET AL 3,450,097 VAPOR DEPOSITION APPARATUS Sheet 2of2 I INVE'NTORS, STANLEY FIRESTONE JOHN MC CARTHY BY 5M A/Z4. C. WATTORNEYS United States Patent Office 3,450,097 Patented June 17, 1969US. Cl. 118-49 7 Claims ABSTRACT OF THE DISCLOSURE A vapor depositionapparatus including a compartmented vapor source defining a tortuousflow path for the evaporant to inhibit particle spatter in thedeposition zone and means within the deposition chamber to sequentiallyfeed, to said source, discrete amounts of material to be evaporated.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes without the payment of anyroyalty thereon.

The present invention relates to deposition of thin films on substratesby vaporization and more particularly to the deposition on substrates ofa relatively homogeneous film from mixtures of materials which havedifferent vaporization temperatures.

The deposition of films on substrates has become an important techniquein the miniaturization of electronic components. Miniature printedelectronic circuits and components can be formed on substrates bydepositing these circuits or components on the substrate in the form ofa film. One particularly critical area is in the formation of resistanceelements by film deposition. Due to the extreme thinness of the films,resistance elements normally have to be made relatively long in size.Since, as a practical matter resistance elements in circuits formed byfilm deposition have taken up a relatively high proportion of thecircuit area, recent emphasis has been placed upon finding materials ofhigh electronic resistance in order to form small stable high resistanceelements. One type of material that could be used successfully is acermet. Cermets are a substance consisting of a metal in a ceramic suchas metallic oxide, carbide or nitride. One example of a cermet that isparticularly useful in the formation of resistance elements is a mixtureof chromium and silicon monoxide.

While cermets have the necessary properties to form the desired highresistance film, their deposition as a homogeneous film has presentedproblems because the elements of a cermet mixture have widely differentvapor pressures or thermal evaporation levels. In the past, theexistence of these different thermal evaporation levels has causeddifficulty in depositing homogeneous films of the cermet material. As isreadily apparent, an unevenly deposited film is undesirable because itdoes not have the desired uniform electrical properties and iselectrically unpredictable.

Because of the composition of cermets it is necessary to employ hightemperatures often in the order of 1600 2000 C. and perform the actualdeposition under conditions approaching a vacuum. Working at such hightemperatures amplifies the problem of working with a mix ture ofmaterials of different thermal evaporation levels. Also, the necessityof working in a vacuum increases the difiiculty of handling materials.

In the past, two approaches have been taken. One of these methods hasbeen to preheat a metal surface often called a source and to feed thematerial to be evaporated in powdered form toward the source. Thesubstrate that was designed to receive the film was placed above thesource. In this arrangement, the placement of the feeder and substrateis very critical. Surrounding the heat source is a thermal layer thatvaries in temperature inversely with the distance from the source. Thecloser the feeder is positioned to the source, the more likely thepowder portion with the lowest vaporization temperature will vaporizewithin the feeding mechanism. To the extent that vaporization takesplace within the feeding mechanism, it will destroy the ability toobtain the desired film consistency. Moving the feeder further away fromthe heat source creates other disadvantages. When the powder is fedtowards the heat source, the convection currents caused by the thermallayer will deflect some of the particles away from the heat zonecompletely and cause other particles to be propelled upward, orspattered, and eventually deposited on the substrate. The deflection ofparticles away from the heat zone changes the composition of the film tobe deposited on the substrate. The spattering of particles directly ontothe substrate also harmfully affects the composition of the film. In aneffort to eliminate spattered particles from being deposited on thesubstrate, the substrate is usually placed quite far from the heatsource. This necessitates the use of exceptionally large and expensiveequipment and slows down the rate of film deposition. In addition to theabove difficulties, the difference in vaporization temperatures causesthe following problem. Since there is a temperature gradient around theheat source, the particles Will have to travel varying distances towardsthe heat source before they are veporized. This distance will dependupon the vaporization temperature. The effect of this difference is tocause the different materials to vaporize at different times.

The second common way of depositing a film is to place the mixture to bedeposited on the substrate into an unheated crucible or box and thenraise the temperature to a temperature above the vaporizationtemperature of all of the elements of the material to be deposited.Where the mixture contains materials of widely different thermalevaporation levels, the materials will be deposited sequentially ratherthan homogeneously since one of the materials will vaporize before theother.

The general purpose of the invention is to provide means for depositinga homogeneous film on a substrate employing feeding and evaporatingmeans possessing none of the aforedescribed disadvantages. To attainthis, the present invention contemplates unique means for feeding andvaporizing the material to be deposited.

An object of the present invention is the provision of means fordepositing a homogeneous film from materials of different vaporizationtemperatures.

Another object is to provide a means for making an electrical resistanceelement by vaporization of cermets.

A further object of the invention is the provision of a simplified heatsource for the evaporation of materials in powdered form.

Still another object is to provide a simplified heat source for theevaporation of materials in pellet form.

Yet another object of the present invention is the provision ofsimplified means for feeding material to be evaporated into a heatsource.

The exact nature of this invention as well as other objects andadvantages thereof will be readily apparent from consideration of thefollowing specification and the accompanying drawings in which likereference numerals designate like parts throughout the figures thereofand wherein:

FIG. 1 is a diagrammatic view in side elevation of a system for filmdeposition;

FIG. 2 is an exploded perspective view of a preferred embodiment of aheat source;

FIG. 3 is a perspective view of a modified heat source; and

FIG. 4 is a perspective view of preferred embodiment of a feedingmechanism.

Referring now to the drawings, there is shown in FIG. 1 a vacuum chambercomprising a base housing 12 and a detachable top 14. Base housing 12and top 14 are designed to provide an air tight chamber except for anorifice 16 to which evacuation means (not shown) may be connected.Extending upwardly from the bottom of base housing 12 are a pair ofspaced cylindrical supports 18 and 20. Brackets 22 and 24 arerespectively fastened to supports 18 and by bolts 26 and 28, saidbrackets being Z shaped and made of a rigid electrically conductivemetal with an extremely high melting temperature. Electrical conductors30' .and 32 are within supports 18 and 20 respectively and arranged suchthat they are in electrical contact with brackets 22 and 24 when thebrackets are secured to the supports. The conductors are connected to asource of electric power (not shown). A heat box source 34 is detachablymounted to brackets 22 and 24 by removable fasteners 36 and 38. The heatbox source may be one of several embodiments which will be described indetail hereinafter. A feeding mechanism 40, which is controlled fromoutside the chamber 10 by control means 42, is positioned within thevacuum chamber 10 in such a manner that it can be used to feed thematerial to be deposited on the film or substrate into the input 44 ofheat box source 34. The structural details and position desired in .afeeding mechanism will vary with the type of box source used. Aparticularly advantageous feeding mechanism will be described in detaillater. A rod 46, mounted on base housing 12, has detachably mountedthereon a platform or support 48 which supports the substance 50 onwhich it is desired to deposit the film. The rod and holder are arrangedsuch that the substance on which it is desired to deposit the film ispositioned over the output 52 of the heat box source 34.

Referring now to FIG. 2, there is shown in detail an exploded view ofone embodiment of box heat source 34. The base chamber 54 comprises aflat base 56, sidewalls 58, 60 and end walls 62 and 64. As shown, theend walls 62 and 64 extend beyond side walls 58 and 60 and areterminated by respective outwardly extending flanges 66 and 68. Thewalls forming the box-shaped chamber 54 are fastened together bywelding. A transverse septum 74 extends upwardly from base 56 and ispositioned midway between end walls 62 and 64. The height of septum 74is made slightly less than the width of side walls 58 and 60.

Chamber 54 is provided with a complementary top or cover 76 whichcomprises a plate 78 including downwardly extending side members 80, 82and upwardly extending end members 84, 86, which are terminated byoutwardly extending flanges 88, 90. Corresponding apertures or holes 70,92 and 72, 94 are provided in flanges 66, 88 and 68, 90 so that the top76 and base chamber 54 may be properly aligned and fastened together asan integrated device onto supports 18 and 20 (FIG. 1). Spaced circularinput and output apertures or holes 96 and 100, respectively, 'areprovided in plate 78 as shown. Input hole 96 is bounded by a raisedcircular lip portion 98 and a chimney 102 is welded around aperture 100so that both the lip and chimney extend upwardly from base plate 78.Spaced transverse septums 104 and 106 are provided on the underside ofplate 78 and are terminated short of the side members 80 and 82 suchthat when top 76 is positioned over chamber 54, the septums 104 and 106are on either side of septum 74 and are within the chamber 54. By suchan arrangement, a bafiie is provided between input and output apertures96 and 100. Connecting studs 108 and 110 are afiixed to sides 80 and 82,respectively, and are respectively welded to points 112 and 114 shown inphantom on shield 116 in such a manner that the shield is held in spacedrelation from top 76 when in position.

Shield 116 comprises a U-shaped member having a base 118 and arms 120and 122. Spaced circular apertures 124 and 126 are provided in base 118with their respective centers aligned with the centers of apertures 96and 100 on plate 78, the aperture 124 being slightly smaller thanaperture 96 and aperture 126 being slightly larger than aperture 100.Aperture 124 is bounded by an upwardly extending entrance funnel 130 anda downwardly extending lip 128 which together form a passageway with adiameter slightly smaller than the diameter of lip 98. When shield 116is welded to top 76, chimney 102 passes through and clears hole 126.Chamber 54 is provided with a bottom heat shield 132 which is connectedto chamber 54 by means of studs 134 and 136 which, in turn, are weldedto sidewalls 58 and 60 respectively in such a manner that shield 132 isheld parallel to and spaced apart from flat base 56.

FIG. 3 illustrates another embodiment of the heat box source shown inFIG. 2. In this embodiment the perpendicular entrance funnel has beenreplaced by a cylindrical entrance funnel 138 that meets base 118 at anacute angle such as 45". Welded to the free end of funnel 138 is a coneshaped tip 140. The two embodiments differ in that the first (FIG. 2) isparticularly adapted for the vaporization of materials in pellet formwhile the latter (FIG. 3) is best used with powders.

Referring now to FIG. 4, there is shown a feeding mechanism for use inthe vaporization or vacuum evaporation of materials in pellet form.Supports 142 and 144 are afiixed to the base housing 12 of vacuumchamber 10 and a third support 146 which comprises braces 148 and 150mounted on base housing 12 with cross bar 152 mounted across the braces.A carriage 154 comprising a channel bar 156 with a pair of outwardlydisposed right angle flanges 158, 160 at one end is mounted in vacuumchamber 10 at this end by screw 162 which passes through aperture 164 inflange 158 and into support 144. The other end of the carriage rests onsupport 146. The carriage 154 is mounted with the channel facing upwardand is positioned so that hole 166 in the center piece of channel member156 is positioned over the entrance funnel 130 of the heat source box tobe used. A rectangular bar 168 rests in channel 156 said bar beingprovided with a plurality of circular holes 170 along its length and arectangular slot 172 at one end. Rod 174 is positioned in support 142and is terminated by tongue 176, said tongue being fastened into slot172 in bar 168. Rod 174 is so mounted that it may be longitudinallypositioned which in turn moves bar 168 along channel bar 156. Themovement of rod 174 may be controlled by hand or any suitable controlmechanism such as a solenoid (not shown).

The operation of the invention will now be described. The particularheat source box and feeding mechanism that would be best to employdepends upon the form of the material to be deposited on the substrate.While in the past it has been the practice to feed the depositionmaterial in powder form, surprisingly good results have been obtained bypreforming the deposition material into pellets particularly when a heatbox source of the type described in this application is used. Thefeeding mechanism shown in FIG. 4 together with the heat box illustratedin FIG. 2 are most suitable for deposition material in pellet form. Theheat source box is secured into place as shown in FIG. 1. The pelletfeed is mounted in the vacuum chamber so that the hole 166 in carriage154 is over funnel 130. A pellet of deposition material is placed ineach of the holes 170 of rectangular bar 168. The substrate upon whichthe deposition will take place is positioned on holder 48 and the vacuumchamber 10 is sealed and evacuated. A large electric current is passedfrom a source (not shown) through conductor 30, bracket 22, the heatsource box, bracket 24 and conductor 32. The heat box source which ismade of material with an extremely high melting point such as tantalumis brought to the desired temperature, which is preferably higher thanthe vaporization temperature of each of the materials to be deposited,by

adjusting the size of the current passing through it. Bar 168 is thencaused to move along carriage 154 by means of adjusting rod 174 from theoutside. Eventually, a pellet in one of the holes 170 will reach hole166 and drop into entrance funnel 130 and, in turn, into the preheatedheat box source. The movement of bar 168 is continued and a solidportion of the bar closes funnel 130. Since the diameter of funnel 130and lip 128 is smaller than that of lip 98, the pellet will falldirectly into the box source. In addition the mass and consistency of apellet prevents a portion of the deposition mixture from being deflectedaway from the heat box source. The presence of the heat shield 116prevents the pellets from being vaporized prior to entering the heat boxsource and the spacing between lip 98 and lip 1.28 prevents funnel 130from becoming too hot. When the pellet reaches the inside of the heatbox source it is vaporized and the vapor passes around septums 74, 104and 106, out chimney 102, and is deposited on substrate 50-. Using aseparate exit chimney and entrance funnel together with the blocking offunnel 130 and the use of a baflie means greatly reduces deflection andspattering and as a result increases the consistency of the deposition.Other pellets may be fed as desired.

The heat source box shown in FIG. 3 is best used with powdereddeposition mixtures. When powders are used it is considerably morediflicult to obtain spatter free consistent films. When powders aredropped in directly, the light mass of the material increases theoccurrence of deflected material and spattering. In addition, thefeeding mechanism must be placed very close to the entrance funnel. Asnoted previously, the further the feeder is placed from the funnel thegreater the chance for deflection while the closer it is placed thegreater the chance of vaporization prior to the desired time. Anotherproblem is the hardening of portions of the powder to the funnel. Theentrance funnel in this embodiment does away with these problems. Theangular disposition of the funnel sufliciently removes the feedingmechanism from the heated area to eliminate the problem of priorvaporization in the feeder. In itself, the change in angle would notfully accomplish the desired result because the powder would ordinarilyharden to the sides of the funnel as it approached the opening to theheat box source. However, the location of the funnel on the shieldspaced away from the heat box source keeps the temperature of the funnellow enough to prevent this. With the exception of this difference infunnels the two box sources are identical and share the same advantages.

Thus, it can be seen that the invention not only provides improvedresults but its very simplicity makes the deposition of a film on asubstrate easier by the elimination of many critical problem areas.

What is claimed is:

1. in a vapor deposition apparatus, a heat box source comprising a basechamber, a transverse wall extending from the base of the chamber and oflesser height than the vertical walls which form said chamber whereby tocompartment said chamber, a complementary detachable top for saidchamber provided with an entrance aperture for receiving a material tobe evaporated, an exit aperture for delivery of such material as anevaporant, said apertures communicating 'with respective ones of saidcompartments, heat shield means attached to said detachable top, saidheat shield means being provided with a first and a second aperturecorresponding to said entrance and exit apertures, funnel means mountedon said heat shield bounding said first aperture, electrical means toheat said chamber, and baflie means disposed within respective ones ofsaid compartments and mounted on said top whereby a tortuous flow ofevaporant between the compartments and to the exit aperture is etfectedwithout spatter of nonvapor particles at said exit aperture.

2. A heat box source as claimed in claim 1 wherein said funnel means ismounted perpendicular to said heat shield means.

3. A heat box source as claimed in claim 1 wherein said funnel means ismounted at an acute angle with said heat shield means.

4. The apparatus of claim 1 including means to mount said heat shield onsaid complementary top in spaced relation from said top with the centersof said corresponding apertures aligned, and chimney means mountedaround said exit aperture of the top so as to pass through thecorresponding aperture of the shield means.

5. A heat box source as claimed in claim 4 wherein said end walls extendfurther than said side walls and including outwardly disposed flangesmounted on each of said end walls, end members mounted on said plateextending in a direction opposite said side members, correspondingoutwardly disposed flanges mounted on each of said end members, said endmembers contacting said end walls and said corresponding flangescontacting each other when said complementary top is in place.

6. The apparatus of claim 1 wherein said heat box source is disposed ina vacuum chamber, means in said vacuum chamber to support a substrate,means to feed said material to be evaporated and comprising; a fixedtrack member disposed in an upper section of said vacuum chamber, anaperture in said track member and disposed in alignment with said funnelmeans, a bar slidable on said track, at least one aperture in said barwhereby to form with the face of the track member a container forstoring material to be evaporated, and means to move said bar along thetrack member whereby to align said bar aperture with the track apertureto deliver said stored material to the funnel means.

7. The apparatus of claim 6 wherein the bar member has a plurality ofaligned apertures to form a plurality of containers for storing materialto be evaporated and wherein said means to move the bar may sequentiallydeliver said material to the funnel means.

References Cited UNITED STATES PATENTS 231,038 8/1880 Harris ll848 X1,930,869 1 0/193 3 Baden 219271 2,053,781 9/ 1936 Reichel ll8482,940,873 6/ 1960 Toohig ll849 X 3,233,577 2/1966 Allen 11849.13,244,857 4/1966 Bertelsen et al 219 -275 3,246,627 4/ 1966 Loeb et al.ll849 3,354,607 11/1967 Lakso 53-08 FOREIGN PATENTS 742,066 12/ 1955Great Britain.

OTHER REFERENCES IBM Techanical Disclosure Bulletin, Evaporation Bowlfor Silicon Monoxide, vol. 2, No. 3 (October 1959), pp. 2728, D. S.West.

MORRIS KAPLA N, Primary Examiner.

US. Cl. X.R. 219-271

